The measurement of the visual field in addition to the measurement of pressure has an important role in the ophthalmology practice. It is known to use the perimeter of Goldmann for measuring the visual field, which perimeter enables the user to carry out both a kinetic-quantitative and also a static-quantitative examination. This kinetic-quantitative perimetry works with a movable test mark of a specific brightness, with which the points of the same contrast sensitivity are located perpendicularly to the visual field limits to be expected or isopters, which is guaranteed by the free mobility of the test mark in every direction. In the static-quantitative perimetry, the patient is offered a stationary test mark with a specific brightness, which is recognized as a superthreshold at any point in the visual field. Both examining methods are as a rule carried out side-by-side so that a device with which both examining methods can be carried out is advantageous.
The Goldmann perimeter is a cup-shaped projection perimeter with a direct registration of the test mark position. The even and constant illumination of the inside of the cup is supposed to guarantee during each examination always the same adaption state of the eye. The test mark, with which one determines the stimulus threshold of the light sensed in the central and peripheral visual field portions, is projected from the cup opening onto the base of the cup. Since, however, the head of the patient is fixed exactly onto the center of the cup, it is compulsory that the projection system is arranged eccentrically. Distortions of varying strength of the test mark in dependency of the respectively chosen test mark position result from this eccentric arrangement. With this not only the shape of the test mark is changed but also its brightness distribution so that sources of error can occur.